1. Field of the Invention
The present invention relates to a firing furnace for burning off binders within a paste layer and a method of manufacturing a plasma display panel using the firing furnace, and more particularly to a firing furnace intended to have the ability to uniformly supply gas containing oxygen to the inside of the firing furnace and a method of manufacturing a plasma display panel using the firing furnace.
2. Description of the Related Art
For example, as is disclosed in Japanese Patent Application No. 11(1999)-025854, a method of manufacturing a plasma display panel (hereinafter, referred to as PDP) includes: forming scanning electrodes and common electrodes on a substrate; forming a layer of a dielectric material and a protection layer of MgO over the scanning electrodes and common electrodes in order to form a front substrate; forming data electrodes on the other substrate; forming a layer of a dielectric material, barrier ribs and phosphor layers over the data electrodes in order to form a back substrate; and bonding the front substrate and back substrate to each other. Furthermore, in the individual steps including forming the aforementioned scanning electrodes and common electrodes, and forming the aforementioned layer of a dielectric material, barrier ribs and phosphor layers, a paste layer is formed on the substrate and then is fired by heat treatment.
FIG. 1 illustrates a schematic view of a conventional firing furnace for sequential processing and a chart diagram indicating temperature distribution in a furnace, in which axis of abscissas denotes substrate location within the firing furnace and axis of ordinate denotes substrate temperature. FIG. 2 is a partial cross sectional view illustrating the conventional firing furnace and FIG. 3A is a front view illustrating gas distribution piping of the conventional firing furnace, and FIG. 3B is a front view illustrating gas exhaust piping.
As shown in FIG. 1, the conventional firing furnace 101 for sequential processing comprises a temperature boosting section 102, temperature maintaining section 103 and cooling section 104, in which the individual sections each have a plurality of furnace compartments 105. Within the firing furnace 101, a substrate 111 of PDP is moved in a direction 112 passing through the temperature boosting section 102, temperature maintaining section 103 and cooling section 104 in this order. The temperature boosting section 102 is a section provided to boost the temperature of the substrate 111 from the room temperature to a firing temperature T and the temperature maintaining section 103 is a section provided to maintain the substrate 111 at the firing temperature T, and the cooling section 104 is a section provided to cool the substrate 111 from the firing temperature T to a lower temperature. The firing temperature T may typically be about 500 to 600° C. The adjacent furnace compartments 105 are coupled to each other through a connection path 110 (refer to FIG. 2). The connection path 110 is provided to allow the substrate 111 pass therethrough. The temperature boosting section 102 is configured so that the furnace compartment 105 located on the downstream side when viewing the substrate 111 in the direction 112 of movement of the substrate is set at higher temperatures. However, in some cases, a plurality of sequentially-arranged furnace compartments 105 may be set at the same temperature. Note that a furnace compartment 105a chosen out of the plurality of furnace compartments 105 and located nearest to the upstream side when viewing the substrate 111 in the direction 112 of movement of the substrate constitutes an entrance of the firing furnace 101 and faces a clean room (not shown). On the other hand, the cooling section 104 is configured so that the furnace compartment 105 located on the downstream side when viewing the substrate 111 in the direction of movement of the substrate is set at lower temperatures.
As shown in FIG. 2, the individual furnace compartments 105 each have a substrate carrier 106 provided therein. In this case, the substrate 111 is placed on a setter 107 and transported together with the setter 107 in the direction 112 by the substrate carrier 106. Furthermore, the individual furnace compartments 105 of the temperature boosting section 102 each have gas distribution piping 108 and gas exhaust piping 109 provided therein. Within each of the furnace compartments 105 of the temperature boosting section 102, the gas distribution piping 108 is located on the downstream side when viewing the substrate 111 in the direction 112 of movement of the substrate and the gas exhaust piping 109 is located on the upstream side. Furthermore, heated dry air 113 is supplied through the gas distribution piping 108 to heat a paste layer (not shown) provided on the surface of the substrate 111 and then almost all of the dry air 113 is exhausted by the gas exhaust piping 109. That is, a direction in which the dry air 113 is moved is opposite to the direction 112 as a whole and the dry air 113 is moved against the movement of the substrate 111. The dry air 113 is supplied at a supply rate (gas distribution rate) of about several tens meters per second, for example, about 20 meters per second. Additionally, the individual furnace compartments 105 each have provided therein a heating apparatus (not shown) for heating the substrate 111.
The substrate 111 is configured to have a paste layer formed on a glass substrate. The paste layer is made from powdered glass and vehicles which are made from resin binders and solvents. The binders would be, for example, resin binders such as nitrocellulose, ethylcellulose and acrylic, and the solvents would be, for example, terpinenol, acetic ester or the like.
Moreover, as shown in FIG. 3A, the gas distribution piping 108 is configured so that a plurality of equally-spaced openings 114 are formed along the longitudinal direction of the piping 108. The openings 114 each have a shape of circle and are the same in size. Furthermore, as shown in FIG. 3B, the gas exhaust piping 109 is configured so that a plurality of equally-spaced openings 115 are formed along the longitudinal direction of the piping 109. The openings 115 each have a shape of circle and are the same in size. The gas distribution piping 108 is configured so that the dry air 113 is supplied via both ends of the piping 108 and then is supplied through the openings 114 to the furnace compartments 105 and the gas exhaust piping 109 is configured so that the dry air 113 is sucked from within the furnace compartments 105 through the openings 115 and exhausted via both ends of the piping 109.
The substrate 111 transported from the clean room first passes through the furnace compartment 105a located nearest to the upstream side. Then, the substrate 111 passes sequentially through the individual furnace compartments 105 and thus passes through the temperature boosting section 102, temperature maintaining section 103 and cooling section 104 in this order. In the individual furnace compartments 105 of the temperature boosting section 102, the substrate 111 is heated by the heating apparatus and at the same time, exposed to the dry air 113 supplied through the gas distribution piping 108.
In the temperature boosting section 102, subjecting the substrate 111 to the heat treatment causes a part of the binders within the paste layer to be burned off, producing water and carbonic anhydride which, in turn, are carried away by the dry air 113. Moreover, the remaining binders within the paste layer and the solvents are not burned off but evaporated and then carried away by the dry air 113. This allows the binders and solvents (vehicle) to be eliminated from the paste layer and further allows the dry air 113 to become air (hereinafter, referred to as contaminated air) containing water, carbonic anhydride, binder component and solvent component. Thereafter, the temperature maintaining section 103 maintains the substrate 111 at the firing temperature T and fires the paste layer. Subsequently, the cooling section 104 cools the substrate 111 from the firing temperature to around the room temperature.
However, the above-described conventional techniques have the following problems. In recent years, as a PDP grows in size, a substrate for PDP also is growing in size. This increases the width of a firing furnace and the length of gas distribution piping laid within the firing furnace, causing difficulty of blowing dry air out uniformly through openings along the entire length of the gas distribution piping. As a result, one problem arises from the fact that variations in the degree to which the paste layer formed on the substrate of PDP is fired occur.